Adaptive multi-mode harq system and method

ABSTRACT

HARQ methods and systems and systems are provided which adaptively switch between two modes such as an NCP (non-complete puncture) mode, and a SAW (stop and wait) mode. Advantageously, this is done to avoid buffer overflow associated with ongoing NCP, and the delay associated with SAW. The switch between the modes can be performed on the basis of any number of criteria. These may include buffer size, consecutive negative acknowledgements in respect of either of the modes, length of time in one or the other mode, to name a few examples.

RELATED APPLICATIONS

[0001] This application claims the benefit of prior U.S. ProvisionalApplication No. 60/340,024 filed on Dec. 10, 2001 and 60/342,946 filedon Dec. 21, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to systems and methods for re-transmittingpackets after they have been initially transmitted and received inerror.

BACKGROUND OF THE INVENTION

[0003] In wireless; communications systems, HARQ(Hybrid-Automatic-Repeat-Request) protocols are responsible for errorcontrol between transmitters and receivers.

[0004] One common existing approach is referred to as the “stop andwait” (SAW) approach involves the insertion of the re-transmit packetinto the normal packet transmission flow, with the sequence of schedulednormal packet transmission stalled to allow re-transmission of theerroneous packet. One problem with this approach is that the re-transmitpackets take away from the bandwidth available for new transmissions,and the re-transmit packets introduce delay into all subsequentre-transmissions. This; approach is shown in FIG. 1A where the packetsnumbered “1” to “4” to be transmitted are generally indicated by 20, andthe stream of actual packet transmissions is indicated generally by 22,and the acknowledgement sequence is indicated at 24. After a NAK(negative acknowledgement) indicating failed transmission is received inrespect of packet “1”, the packet is re-transmitted after packet “2”,with the remaining packets being forced to wait. When an ACKacknowledgement) is received indicating successful transmission ofpacket “2”, packet “3” is then transmitted and so on.

[0005] In another existing approach shown in FIG. 1B, rather thanre-transmitting a packet identical to the original packet, there-transmitted packets contain the entire systematic content of theoriginal packet but contain different versions of the redundancies.Thus, in the packet flow 30 of FIG. 1B, packet “1(1)” is are-transmitted version of packet “1” with a first revised set ofredundancies, and the packet “1(2)” is a re-transmitted version ofpacket “1” with a second revised set of redundancies. Thesere-transmitted packets are shown inserted directly within thetransmission flow, so this is a stop and wait scheme. Alternatively, there-transmission flow can be transmitted on a separate physical channelas shown in FIG. 1C.

[0006] Another approach which has been employed is referred to as AAIR(asynchronous adaptive incremental redundancy). In this approach,packets are divided up into three segments, the first containing aSystematic component and some redundancy, and the second and thirdsegments only containing redundancy. In the event the initial packettransmission is in error, the first segment is re-transmitted. If thepacket still cannot be recovered, the second segment is re-transmitted.Finally, if the packet still cannot be recovered, the third segment isre-transmitted. The original transmission plus the re-transmittedsegments are combined using Chase and incremental redundancy (IR)combining.

[0007] U.S. patent application Ser. No. 10/074,701 entitled “PartialPuncture Re-Transmission” filed Feb. 13, 2002 and commonly assigned withthis application hereby incorporated by reference in its entirety,teaches another incremental redundancy approach referred to as theNon-complete puncture (NCP) approach in which for re-transmission,re-transmit packets are formed with different versions of redundancy asin the example of FIG. 1B. Each re-transmit packet is divided into alarge number of segments or sub-packets, for example six per packet. Thebits of these sub-packets, one sub-packet at a time, are inserted bypuncturing them into the regular transmission stream, thereby having noeffect on the regular transmission schedule. One issue with thisapproach is that it is possible that a large number of re-transmissionswill be required before sufficient redundancy is re-transmitted to allowsuccessful reception. For example, compared to simply re-transmittingthe packet three times, re-transmission using ⅙^(th) sub-packets malttake up to 18 time slots and this delay may be too long. Another issuewith this approach is that at the receiver, the entire “soft packet”received so far needs to be stored, and this can lead to significantbuffer requirements since many packets can be transmitted and manyre-transmissions may be occurring simultaneously. This approach doesoffer the benefit of time diversity. This NCP approach is depicted inFIG. 2 where the regular packet flow is indicated generally by 40, andthe ACK/IZAK stream is indicated at 42. For packet “1” which wasreceived in error, a re-transmit packet 44 is generated. This isreferred to as “1(1)” because subsequent re-transmit packets may beemployed which would contain different versions of redundancy. Alsoshown is a re-transmit packet 46 for packet “3” which was also receivedin error. Each of these re-transmit packets is in turn is divided intorespective sets of sub-packets, the illustrated example showing sixsub-packets per re-transmit packet. These re-transmit sub-packets arethen inserted by puncturing, one sub-packet at a time in each slot ofthe regular transmission. Thus, the first sub-packet of the firstre-transmit packet 44 is inserted into by puncturing packet “3”, thesecond sub-packet of the first re-transmit packet 44 is inserted bypuncturing into packet “4”, and so on.

SUMMARY OF THE INVENTION

[0008] HARQ methods and systems and systems are provided whichadaptively switch between two modes such as an NCP (non-completepuncture) mode, and a SAW (stop and wait) mode. Advantageously, this isdone to avoid buffer overflow associated with ongoing NCP, and the delayassociated with SAW. The switch between the modes can be performed onthe basis of any number of criteria. These may include buffer size,consecutive negative acknowledgements in respect of either of the modes,length of time in one or the other mode, to name a few examples.

[0009] According to one broad aspect, the invention provides a method ofperforming packet re-transmission comprising: providing a firstre-transmission mode and a second re-transmission mode; and switchingbetween executing the first re-transmission mode and executing thesecond re-transmission mode.

[0010] In some embodiments, the first re-transmission mode is a parallelre-transmission mode and the second re-transmission mode is a stop andwait (SAW) mode.

[0011] In some embodiments, a switch from the first mode to the secondmode occurs after transmission of a predetermined number of first modetransmissions in respect of a given packet.

[0012] In some embodiments, a switch from the first mode to the secondmode occurs as a function of one or more system parameters.

[0013] In some embodiments, the one or more system parameters comprise areceiver buffer occupancy by first mode content.

[0014] In some embodiments, the switch from the first mode to the secondmode occurs when the receiver buffer occupancy exceeds a threshold.

[0015] In some embodiments, the SAW mode comprises: defining a pluralityof re-transmit packets for a packet to be re-transmitted, each havingdifferent redundancies; and inserting the re-transmit packets one at atime into a normal packet flow in place of normal packets.

[0016] In some embodiments, the parallel re-transmission mode comprises:defining at least one re-transmit packet for a packet to bere-transmitted; dividing each re-transmit packet into a respectiveplurality sub-packets; transmitting a subset of the sub-packets of oneof the re-transmit packets using a transmission channel parallel to anormal packet flow.

[0017] In some embodiments, the parallel re-transmission mode is anon-complete puncture (NCP) mode in which transmitting a subset of thesub-packets of one of the re-transmit packets using a transmissionchannel parallel to a normal packet flow comprises inserting the subsetof the sub-packets of one of the re-transmit packets into one or morenormal packets of a normal packet flow by puncturing the one or morenormal packets with bits from the subset of sub-packets.

[0018] In some embodiments, each re-transmit packet contains systematiccontent from an original packet with different redundancies.

[0019] In some embodiments, the method further comprises transmittingcontrol information indicating which of the first re-transmission modeand second re-transmission mode is a current mode of operation ofre-transmission.

[0020] In some embodiments, the method further comprises transmittingcontrol information indicating for SAW mode which re-transmit packet isbeing transmitted.

[0021] In some embodiments, the method further comprises wherein for agiven NCP transmission, the subset of sub-packets can have a variablesize, the method further comprising transmitting control informationindicating for NCP mode how many NCP sub-packets are in the subset.

[0022] In some embodiments, the entire subset is punctured into a singlenormal packet.

[0023] In some embodiments, the method further comprises providing afirst acknowledgement channel in respect of the first mode and a secondacknowledgement channel in respect of the second mode.

[0024] In some embodiments, the method further comprises performing aswitch between modes as a function of the first acknowledgement channel.

[0025] In some embodiments, a switch between modes as a function of thefirst acknowledgement channel is performed after a predetermined numberof negative acknowledgements are received in respect of first modeoperation.

[0026] In some embodiments, the method further comprises performing aswitch between modes as a function of the second acknowledgementchannel.

[0027] In some embodiments, a switch between modes as a function of thesecond acknowledgement channel is performed after a predetermined numberof negative acknowledgements are received in respect of second modeoperation.

[0028] According to one broad aspect, the invention provides atransmitter adapted to performing packet re-transmission by: providing afirst re-transmission mode and a second re-transmission mode; antiswitching between executing the first re-transmission mode and executingthe second re-transmission mode.

[0029] In some embodiments, the first re-transmission mode is a parallelretransmission mode and the second re-transmission mode is a stop andwait (SAW) mode.

[0030] In some embodiments, a switch from the first mode to the secondmode occurs after transmission of a predetermined number of first modetransmissions in respect of a given packet.

[0031] In some embodiments, a switch from the first mode to the secondmode occurs as a function of one or more system parameters.

[0032] In some embodiments, the one or more system parameters comprise areceiver buffer occupancy by first mode content.

[0033] In some embodiments, the SAW mode comprises: defining a pluralityof re-transmit packets for a packet to be re-transmitted, each halvingdifferent redundancies; and inserting the re-transmit packets one at atime into a normal packet flow in place of normal packets.

[0034] In some embodiments, the parallel re-transmission mode comprises;defining at least one re-transmit packet for a packet to bere-transmitted; dividing each re-transmit packet into a respectiveplurality sub-packets; transmitting a subset of the sub-packets of oneof the re-transmit packets using a transmission channel parallel to anormal packet flow.

[0035] In some embodiments, the parallel re-transmission mode is an NCPmode in which transmitting a subset of the sub-packets of one of there-transmit packets using a transmission channel parallel to a normalpacket flow comprises inserting the subset of the sub-packets of one ofthe re-transmit packets into one or more normal packets of a normalpacket flow by puncturing the one or more normal packets with bits fromthe subset of sub-packets.

[0036] In some embodiments, a transmitter is adapted to transmit controlinformation indicating which of the first and second mode is a currentmode of operation of re-transmission, and to transmit controlinformation indicating for SAW mode which re-transmit packet is beingtransmitted.

[0037] In some embodiments, a transmitter is further adapted to receivea first acknowledgement channel in respect of the first mode and asecond acknowledgement channel in respect of the second mode.

[0038] In some embodiments, a transmitter is further adapted to performa switch between modes as a function of the first acknowledgementchannel, the second acknowledgement channel, or a combination of thefirst acknowledgement channel and the second acknowledgement channel.

[0039] According to one broad aspect, the invention provides a packetre-transmission system comprising: first re-transmission mode meansproviding a first parallel re-transmission mode; second re-transmissionmode means providing a second stop and wait re-transmission mode; andmode switching means for switching between executing the first parallelre-transmission mode and executing the second stop and waitre-transmission mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Preferred embodiments of the invention will now be described withreference to the attached drawings in which;

[0041]FIG. 1 provides an illustrative definition of three conventionalpacket re-transmission methods;

[0042]FIG. 2 provides an illustrative definition of a non-completepuncture re-transmission method;

[0043]FIG. 3 provides an illustrative example of a re-transmissionmethod provided by an embodiment of the invention and an example of anassociated forward/reverse link control signaling;

[0044]FIG. 4 is a chart of an example set of adaptive re-transmissionstrategies;

[0045]FIG. 5 is a flowchart of an example method of switching betweenadaptive re-transmission modes;

[0046]FIG. 6 is a flowchart of another example method of the adaptiveswitching between two re-transmission modes;

[0047]FIG. 7 is an illustrative example of the how buffer size is usedto switch between re-transmission modes, according an example of oneembodiment of the invention;

[0048]FIG. 8 provides example performance results consisting ofthroughput per user versus geometry using proportional fairnessscheduling;

[0049]FIG. 9 provides example performance results consisting ofthroughout per user versus geometry using round-robin scheduling;

[0050]FIG. 10 provides example performance results consisting of a PDFversus the number of NCP sub-packets with either proportional fairnessor round-robin scheduling;

[0051]FIG. 11 provides example performance results consisting of a CDFversus receiver buffer size with proportional fairness scheduling;

[0052]FIG. 12 provides example performance results consisting of a CDFversus receiver buffer size with round-robin scheduling;

[0053]FIG. 13 is an illustrative example of split sub-packetre-transmission;

[0054]FIG. 14 is a flowchart of an example of receiver operation forsingle channel operation for SAW mode; and

[0055]FIG. 15 is a flowchart of an example of receiver operation forsingle channel operation for NCP mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0056] A first embodiment of the invention provides a re-transmissionmethod having some of the benefits of the above-introduced NCP approach,without the drawback of potentially very high delay. In this embodiment,after an error in an initial packet transmission has occurred,incremental redundancy is employed to transmit re-transmit packets usingany suitable parallel re-transmission mode. Preferably, the re-transmitpacket is the failed packet, or a portion of a packet having the samesystematic content but different redundancy. By parallelre-transmission, it is meant that any channel can be used which does notintroduce delay into the regular packet transmission. Thus, this wouldinclude the puncturing approach or a separate physical channel forexample.

[0057] For a given packet, after a set number of packet re-transmissionsor some other criteria is satisfied, in order to cap the delay, a switchfrom the parallel transmission mode to the stop and wait approach ismade. This results in the benefits of time diversity and minimalthroughput impact being realized during the packet re-transmissionperiod, but with a switch being made to avoid too high a delay fromoccurring for a given packet.

[0058] Preferably, non-complete puncture (NCP) HARQ is used for theparallel transmission mode. NCP has been proposed to improve the systemperformance for HARQ re-transmission. This technique is extremelypowerful when the received CIR is large enough. However, in case of lowreceived CIR, the benefit is limited because there is not enough energyto be contributed to NCP packet storage. To solve this problem, anoptimum maximum number of NCP packets can be determined, which dependson the received geometry (corresponding to the long term average CIR).If the geometry is large enough, we may choose a large number for NCPsub-packet transmission and vice versa.

[0059] However, it is not easy to estimate the user geometry. In orderto deal with such a problem, in another embodiment of the invention, anadaptive NCP-HARQ is provided which switches between two HARQ protocolsbased on the receiver buffer size. This works because the receiverbuffer size depends strongly on the received CIR corresponding to usergeometry.

[0060] In this case, the adaptive NCP-HARQ is an adaptive transmissionmethod which switches between NCP-HARQ and normal HARQ (for example,stop and wait HARQ (SAW-HARQ)) based on the occupied receiver buffersize. That means, it the occupied receiver buffer size is less than apredetermined level, the NCP-HARQ transmission should be continued.Otherwise, stop NCP-HARQ and switch to normal HARQ transmission such asSAW-HARQ transmission.

[0061] Referring now to FIG. 7, the maximum receiver buffer 700 isdefined as the size of a buffer provided for storing the NCP content forHARQ re-transmission, NCP content being the memory being used to storefailed packets before or after combining with one or more NCPsub-packets. In other words, if the total NCP content is over thatlevel, this buffer has no space to store new failed packets. TheNCP-HARQ zone 702 is defined as a zone as a function of buffer occupancywhere the NCP-HARQ is implemented. The SAW-HARQ zone 704 is defined as azone as a function of buffer occupancy, where the SAW-HARQ isimplemented instead of NCP-HARQ. A threshold 706 is shown for switchingbetween NCP and SAW. This threshold, together with the received bufferoccupancy determine whether the transmitter should use NCP-HARQtransmission or SAW-HARQ transmission.

[0062] There are at least two benefits to use adaptive NCP-HARQ.Firstly, it can avoid the overflow of the receiver buffer. Secondly, itcan be used to efficiently transmit data packets under different channelconditions (low and high geometry, or low and high Doppler spread).

[0063] In summary, the sub-packet re-transmission approach is employeduntil the available buffer memory becomes smaller than a threshold atwhich point, a switch to the stop and wait approach is made. Switchingto the SAW approach will relieve the buffer because no new data flow isbeing transmitted during re-transmissions, in contrast to the NCPapproach characterized by constant re-transmission of new data.

[0064] For example, packet size might be 19200 bits, requiring 19200×4bits of buffer space (accounting for the required soft bits foxincremental redundancy combining) per packet, and the buffer size mightbe 1 Meg, allowing for the storage of about 13 packets in total. Inorder to accommodate a larger number of packets in re-transmissionstate, a larger buffer would be required. Instead of providing a largerbuffer, after the buffer becomes filled to some threshold, for example80%, a switch to the SAW method is made to relieve the buffer. Thisswitch (can be made until the buffer size drops below the threshold, ordrops below another threshold smaller than the initial switch threshold,thereby providing some hysterisis, and avoiding rapid switching back andforth between modes.

[0065] More generally, any suitable criteria may be used to trigger theswitching back and forth between the two approaches. The buffer size isvery easy to measure and as such is easily implementable. For example,in another approach, the long term average C/I is measured, and as thelong term average C/I becomes low, for example lower than a threshold, aswitch is made from the NCP approach to the SAW approach.

[0066] Two embodiments have been described for re-transmission. In orderfor an overall system to function effectively, it is desirable to informthe receiver when switches between modes are going to occur such thatthe received packets can be processed accordingly. Preferably, a controlsignalling channel is provided for communicating these mode changes fromthe transmitter to the receiver.

[0067] A detailed example of the invention featuring a control channelwill now be described with reference to FIG. 3. In this embodiment, asdescribed below, while in NCP mode, a variable number of sub-packets isemployed. The re-transmission sub-packet is associated with anidentification number called a SPID (sub-packet identifier). The decoderuses the SPID to perform correctly the code combining. The SPID is alsoused to indicate the size of the split sub-packet set.

[0068] Two modes or operation are illustrated, each mode of operationhaving a mode identifier, indicated by a first mode Mode-ID=0 300 whichis a SAW mode, and a second mode Mode-ID=1 302 which is an NCP mode. Asingle mode bit can be used to indicate the current Node of operation,and this can be sent on a forward signalling channel. For SAW mode 300,an original packet “1” 304 is shown, together with three subsequentre-transmission versions “1(1)” 306, “1(2)” 308 and “1(2)” 310 each ofwhich contain different versions of redundancy. While in the first mode300, SAW HARQ is performed, so an example sequence of transmittedpackets 314 is “1”, “2”1, “1(1)”, “3”, “11(2)”, “4”. Upon receipt of aNAK in respect of a given packet, a re-transmit packet is sent. Uponreceipt of an ACK, a new packet is sent. It is noted that in theillustrated examples the normal transmit packets and associatedre-transmit packets are all shown to be the same size. More generally,the transmit stream may consist of a sequence of packets/re-transmitpackets of wearying size.

[0069] While in SAW mode, the forward control channel is used toindicate whether a given packet is a new packet, or what version of are-transmit packet it is. In the illustrated example, a two bit SPID(sub-packet identifier) is used to this effect, with SPID=00 indicatingthe original packet 304, SPID=01 indicating the first re-transmit packet306, SPID=10 indicating the second re-transmit packet 308, and SPID=11indicating the third re-transmit packet 310. In the example, the controlchannel 312 contains a sequence of SPIDs 00,00,01,00,10,00 which areused to identity the type of packets in the sequence 314, namely a newpacket, a new packet, a first re-transmit packet, a new packet, a secondre-transmit packet, and a new packet. Of course any suitable method ofindicating this may be employed.

[0070] In the second mode of operation 302, each re-transmit packet isfurther divided into sub-packets, for example eight sub-packets perre-transmit packet. A given NCP re-transmission for the originalre-transmit packet consists of transmitting a subset or all of thesub-packets of the re-transmit packet punctured into one or more normaltransmit packets. In the illustrated example, in NCP mode, for a givenNCP re-transmission, two, four or eight sub-packets are sent in whichcase the sub-packets are organized into subsets of two, four or eightrespectively. In the illustrated example, the re-transmit packet “1(1)”306 is shown organized into subsets of either two 320, four 322, oreight sub-packets 324.

[0071] While in NCP mode, in the illustrated example the forward controlchannel is used to indicate how many sub-packets are in a subset andwill be transmitted as part of an NCP re-transmission. In theillustrated example, a two bit SPID is used to this effect, with SPID=00indicating no sub-packets are being transmitted, with SPID=01 indicatingthere is a subset SET-1 of two sub-packets, SPID 10 indicating thatthere is a subset SET-2 of four sub-packets, SPID=11 indicating thatthere is a subset SET-3 of eight sub-packets. This is particularlyadvantageous for systems with variable packet size. A larger packet willallow the puncturing of a larger number of bits, and thus canpotentially accommodate more punctured sub-packets than a smallerpacket. In some systems, such as systems with fixed packet size, it isnot necessary to provide different numbers of sub-packets in a NCPre-transmissions, and a constant number (one or some other number) ofsub-packets is punctured for each packet with NCP content.

[0072] In NCP mode, a sequence of packets 330 consisting of packets “1”,“2”, “3”, “4”, “5”, and “6” is shown. The control channel 332 (which canbe the same as control channel 312 used for SAW mode) is showncontaining a sequence of SPIDs 00,00,01,00,10,00,10. This means that thefirst, second, fourth and sixth packets have SPID 00 and do not containany NCP content. The third packet “3” has SPID 01 and has been puncturedto contain two NCP sub-packets of a re-transmit packet associated withpacket “1” for which a NAK was received back from the receiver. Thefifth packet “5” has SPID 10 and has been punctured which foursub-packets of a re-transmit packet associated with packet “3”. In theseexamples, the NCP re-transmission sub-packets of a given re-transmissionare all punctured into one normal flow packet, however, as indicatedabove, they may be spread over multiple packets in some embodiments.

[0073] Depending upon the amount of puncturing, a limit of one or moresub-packets may be imposed for insertion into a given packet.Preferably, only one sub-packet is inserted per slot. In this case, fordifferent size subsets of sub-packets as identified by SPID 332, thepunctured re-transmission would span over different lumbers of packets.For this example, Set-1 320 would span two packet lengths instead ofjust one as illustrated, and Set-2 322 would span four packet lengthsinstead of just one as illustrated.

[0074] The mode identifier and the SPID sequence can be sent over anysuitable control channel. In FIG. 3, the subsequent re-transmissionsub-packets are identified with the SPID and the non-complete-puncturedset of sub-packets are also identified by the SPID with respect to theirnumber. Some advantages of the SPID for both mode-0 and mode-1 are thata single bit, namely the Mode-ID, can be used to perform the transitionfrom one operational mode to another at any time. This single bit can betransmitted with minimum signaling, and therefore with minimum impact onRF capacity.

[0075] In the reverse direction, preferably two acknowledgement channelsare provided, a first “primary acknowledgement” channel in respect ofSAW mode, and in respect of new packets transmitted during NCP mode, anda second “secondary acknowledgement” channel in respect of NCPsub-packets. Either an AMOK or NAK can be sent on either of thesechannels to indicate successful or unsuccessful decoding respectively.Any suitable physical realization of these channels can be employed, andthey could be combined on a single channel and/or as part of some otherreverse channel. Preferably, a single ACK/NAK is sent on the primaryacknowledgement channel for each normal flow packet. Also, a singleACK/NAK is sent on the secondary acknowledgement channel for each NCPre-transmission. If subsets of two sub-packets constitute one NCPre-transmission, then a single ACK/NAK is sent after an attempt todecode the associated packet has been completed.

[0076] In another embodiment, the primary and secondary acknowledgementchannels are used as the, or another, trigger for switching between HARQmodes. For example, adaptive mode transitions can be implemented whichwill allow speeding up the protocol recovery when some number ofconsecutive NAKs occurs in either the primary or the secondary reverselink ACK channels. Two examples, 350,352 are shown which show paralleltime lines for the mode, SPID, primary acknowledgement channel andsecondary acknowledgement channel.

[0077] In the first example 350, a transition from NCP mode to SAW modeis made after some number of normal packets are received in error. Inthe illustrated example, after three normal packets are received inerror (as indicated by three primary acknowledgement channel NAKs), aswitch to SAW mode is made. No NCP content is transmitted during SAWmode so the secondary acknowledgement channel is null during this time.This type of transition will deal with the buffer size problem, since itis the accumulation of regular packets which are not incorrectlyreceived (luring the transmission of further new packets which willresult in buffer overflow.

[0078] In the second example 352, a transition from NCP mode to SAW modeis made after some number of NCP re-transmissions are received in error.In the illustrated example, after three NCP re-transmissions arereceived in error (as indicated by three primary acknowledgement channelNAKs), a switch to SAW mode is made. No NCP content is transmittedduring SAW mode so the secondary acknowledgement channel is null duringthis time. This type of transition will deal with the delay problem,since it is the ongoing transmission of NCP re-transmissions for a givenpacket which will introduce delay into the reception of that packet orof other packets which also require NCP bandwidth.

[0079] In the above described embodiment, a multiplexing the oftransmission and re-transmission flow is constructed by usingpuncturing. Specifically, the sparse re-transmit packet is distributedevenly in time and punctured into the normally scheduled transmissiondata channel (flow). More generally, any parallel re-transmissionchannel approach can be employed. Such a parallel channel can be createdin any dimension, such as parallel time slots, orthogonal code domain orfrequency domain.

[0080] As indicated above, an adaptive re-transmission mode operation isprovided based on the mode-0 and mode-1. The trigger for such atransition can be any suitable trigger defined for a givenimplementation. This allows optimizing the system performance underdifferent conditions. Furthermore, where NCP and SAW are the preferredmodes, more generally any first and second RARQ modes can be employedwhere one has the ability to reduce delay better than the other,sometimes at the expense of causing other packets to wait.

[0081]FIG. 5 shows the flow chart of the adaptive re-transmission modesand transitions between modes. Re-transmission beings in NCP mode,indicated by mode_ID=1, step 5-1. Next, the SPID is determined for eachuser at step 5-2. Recall this determines how many sub-packets per groupare defined. This is set as a function of any suitable parameter(s).Several example parameters are indicated, including geometry, bluffersize, channel type, traffic type and average throughput, although othersmay be employed. Next, NCP mode re-transmission is executed at step 5-3.At step 5-4, a decision is made as to whether or not to switch to SAWmode (mode-0). This can be triggered by implementation specificconditions. In the illustrated example, several triggers including delaybound, buffer overflow, and consecutive NAK's are shown but others mayalternatively be employed, or employed in combination. If it is not timeto switch, operation continues with mode 1 transmission 5-3. Otherwise,the mode is switched to mode 0, and SAW re-transmission mode is executedat step 5-5 until either successful transmission (not shown) or untilthere are no more re-transmit packets as determined by condition block5-6. When that is the case, the packet is a considered erroneous.

[0082]FIG. 6 is a flowchart of a more specific example of the operationof the two re-transmission modes. During step 6-1, the mode is NCP mode,but SPID is 00 since it is the first transmission of a give-n packet. Ifthe packet is decoded correctly (step 6-2), then no re-transmission isnecessary, and the process continues with the next packet back at step6-1. If the packet is not decoded correctly, then at step 6-3,puncturing of the first split sub-packet into a normal packet isperformed. At step 6-4, if the normal packet is correctly decoded, thenthe inserted sub-packet is extracted and combined with previouslyreceived content. If this results in proper decoding of the re-transmitpacket flow (yes path, step 6-8), then the method returns to step 6-1with the normal transmission of another packet. On the other hand, ifthe re-transmit packet is not yet correctly decoded, then if the maximumnumber of re-transmit sub-packets is not yet reached (no path, step6-7), and there is not some other trigger for changing there-transmission mode (step 6-6), then the method continues withpuncturing the next sub-packet into another normal packet at step 6-5.If the maximum number of split sub-packets has been reached (yes path,step 6-7) or some other trigger for mode change has occurred (yes path,step 6-6) then a switch in mode to SAW is performed at step 6-10, and are-transmit packet is sent. If the combined packet is then correctlydecodable (yes path, step 6-11) then the method returns to step 6-1. Ifnot, then another re-transmit packet is sent at step 6-12. If thecombined packet is then correctly decodable, the method returns to step6-1. Otherwise, the packet is counted as a residual encoder packet errorat step 6-14.

[0083] It is noted that if there are multiple packets waiting for NCPre-transmission, in one embodiment, NCP re-transmissions are conductedfor the oldest such packet requiring re-transmission until successfultransmission. Round trip acknowledgement delay may result in a windowduring which the oldest packet is awaiting acknowledgement. In thiscase, preferably, the second oldest packet requiring re-transmissionscheduled for NCP re-transmission, and so on.

[0084] Simulation Results

[0085] To illustrate the effectiveness of the new systems and methodsprovided by embodiments of the invention, various simulations have beenperformed. It should be emphasized that these simulation results relateto an example set of parameters and similar results cannot be guaranteedin the more general application.

[0086]FIGS. 8 and 9 show the throughput performance with proportionalfairness and round-robin schedulers respectively as a function ofgeometry (long term average CIR) with channel model C (see 1×EV-DVevaluation methodology, addendum (V6) Jul. 25, 2001). Referring firstlyto FIG. 8, three sets of results are shown for proportional fairnessscheduler simulations. A first set of results, indicated by 800 is for ahybrid NCP/SAW scheme in which a switch from NCP to SAW takes placeafter the transmission of eight NCP sub-packets. A second set of results802 is for conventional SAW re-transmission. A third set of results 804is for adaptive NCP which switches as a function of buffer size to SAWwhen the buffer reaches 0.5 Mbits. Referring also to FIG. 9, three setsof results are shown for round-robin scheduler simulations. A first setof results, indicated by 900 is for a hybrid NCP/SAW scheme in which aswitch from NCP to SAW takes place after the transmission of eight NCPsub-packets. A second set of results 902 is for conventional SAWre-transmission. A third set of results 904 is for adaptive NCP whichswitches as a function of buffer size to SAW when the buffer reaches 0.5Mbits.

[0087] From these results, it can be seen that in both cases there is acrossover between non-NCP system and NCP-HARQ with fixed maximum NCPnumber (the number is eight). This crossover, however, can be removed byusing adaptive NCP-HARQ. This is because when the received geometry islow, NCP-HARQ cannot provide enough energy to recover re-transmissionsub-packet. In this case, the full sub-packet with normal HARQ isrequired. To switch between NCP-HARQ and SAW-HARQ, the adaptive NCP-HARQis necessary. The adaptive NCP-HARQ may adjust the number of NCPsub-packets before switching it into SAW-HARQ mode so that there-transmission can be efficiently performed under different channelconditions including channel model and geometry, and the totalthroughput gain can be significantly improved. (The detailed comparisonis listed in Table 1.

[0088]FIG. 10 shows a PDF (probability density function) as a functionof the number of NCP sub-packets with either proportional fairness (PF)or round-robin (RR) scheduler. From this figure, it can be seen that theprobability of a small number of NCP sub-packets for the adaptiveNCP-HARQ is much higher than for regular NCP-HARQ, while the probabilityof a large number of NCP sub-packets for the adaptive NCP-HARQ is muchlower than NCP-HARQ.

[0089]FIGS. 11 and 12 show a CDF as a function of the receiver buffersize that is used to store the failed sub-packets for NCP-HARQre-transmission, again for proportional fairness scheduling andround-robin scheduling respectively. From these Figures, it can be foundthat although adaptive NCP-HARQ requires a receiver buffer sizes asopposed to non-NCP system, the maximum buffer size can be controlledunder a predetermined level (for example, 0.5 Mbits). This buffer sizeis much lower than that which results in a fixed NCP system.

[0090] Finally, a comparison is made between non-NCP, fixed NCP andadaptive NCP systems as listed in Table 1 below. TABLE 1 Sectorthroughput and average residual FER. Adaptive Gain Gain NCP for for WithWithout BF = 0.5 fixed adaptive NCP NCP Mbits NCP NCP Sector 433.73495.49 558.91 −12.46% 12.80% Throughput 346.81 274.97 352.05   26.13%28.03% (kbps) Average 1.22e− 3.86e− 5.327e−03 — — Residual 04 03 FER4.10e− 1.08e− 4.99e−04 — — 05 03

[0091] This section describes the above described adaptivere-transmission procedures can be used in the 1×EV-DV extensions tocdma200 to support the enhanced forward packet data channel (F-PDCH).These functions are implemented in the F-PDCH Control Function. Thephysical layer re-transmissions consist of two modes. There-transmission mode is indicated to the mobile station by a ARQ_Mode_IDfield in the F-SPDCCH (Forward Secondary Packet Data Control Channel)channel. The two modes are defined as: the full sub-packetre-transmission (ARQ_Mode_ID=0) and split sub-packet puncturedre-transmission (ARQ_Mode_ID=1).

[0092] In the split sub-packet punctured re-transmission, the incomingnew encoder packets are scheduled independent to the re-transmit packet.The re-transmit sub-packet is generated the same as in the case whenARQ_Mode_ID=0. The re-transmit sub-packet is further split into 8fragments, “split sub-packets”. A sub-set of these split sub-packets (2,4, or 8) is punctured uniformly onto the parity part of the incoming newencoder packet without stalling the new encoder packet scheduling andtransmission. Two separate ACK/NAK signallings are generated from mobilestation to acknowledge the new encoder packet and the re-transmit splitsub-packet.

[0093] When the first sub-packet from an encoder packet is transmitted,SPID on the F-SPDCCH is set to too. If the scheduled mobile stationdetects control information directed towards it on the F-SPDCCH (ForwardPrimary Packet Data Control Channel) and F-SPDCCH and succeeds indecoding the sub-packet, the mobile station sends an ACK on the ReversePrimary Acknowledgment Channel (R-PACKCH). No further sub-packets ofthis encoder packet are transmitted. If the mobile station detectscontrol information on the F-PPDCCH and F-SPDCCH but is not successfulin decoding the sub-packet, it sends a NAK on the R-PACKCH. In thiscase, when the mobile station is scheduled for service again, theincoming new packet is transmitted by the base station and there-transmission of split sub-packets (e.g. 4 split sub-packets) arepunctured onto the scheduled consecutive (4) encoder packets. The numberof split sub-packets for puncturing onto the consecutive scheduledencoder packets is signaled to the mobile station by using the SPIDfield in the F-SPDCCH, namely SPID=01 for 2 split sub-packets, SPID-10for 4 split sub-packets, SPID=11 for a split sub-packets. By this;definition, SPID=00 indicates no split sub-packet puncturing, otherwise,puncturing is performed. An example of parallel channel operation and 8split sub-packets puncturing with early termination of Reverse SecondaryAcknowledgment Channel (R-SACKCH) is shown in FIG. 13.

[0094]FIG. 14 slows a detailed example of the receiver operation forsingle channel operation for ARQ_(—Mode)_ID=0. A brief description ofthe flow chart follows. When the receiver is waiting for a NEWsub-packet (SPID=1001) if a new received packet is a NEW sub-picket(yes-path, step 14-2) and the receiver attempts to decode it at step14-4. If the decoding is successful (yes path, step 14-5) it transmitsan ACK (step 14-6) and then waits for the next NEW sub-packet back atstep 14-1. If the decoding is unsuccessful (no path, step 14-5), ittransmits a NAK at step 14-7, stores the received sub-packet forsubsequent combining with re-transmissions, and waits to receive aCONTINUE sub-packet (SPID≠‘00’) at step 14-8. If the receiver receives aCONTINUE sub-packet while waiting for one (yes path, step 14-9), itattempts decoding by combining the received sub-packet with storedinformation at step 14-10 If the decoding is successful, it transmits anACK and waits for the next NEW sub-packet, while if decoding isunsuccessful, it transmits a NAK and then waits for the next CONTINUEsub-packet.

[0095] For the case when a receiver receives a NEW sub-packet whilewaiting for a CONTINUE (“new path”, step 14-9), the receiver abandonsrecovery of the previous encoder packet and attempts to decode theencoder packet from the new received sub-packet at step 14-4.

[0096] When a receiver receives a CONTINUE sub-packet while waiting fora NEW (“continue” path, step 14-2), the receiver discards the receivedsub-packet, sends an ACK at step 14-3 and then continues to wait for aNEW sub-packet.

[0097]FIG. 15 shows an example of receiver operation for single channeloperation for ARQ_Mode_ID=1 which begins by waiting for a sub-packet15-1. At step 15-2, the sub-packet is decoded. If the packet is thensuccessfully decoded at step 15-3 (yes path), then an ACK is sent atstep 15-4 on the primary acknowledgement channel. If not, then an NAK issent at stop 15-5. If split sub-packet puncturing is employed (yes path,step 15-6), then the split sub-packet is extracted (step 15-6) andcombined with previous sub-packets (step 15-8). If the packet issuccessfully decoded at step 15-9, then an ACK is sent on the secondaryacknowledgement channel at step 15-10 and the method returns to waitingfor the next sub-packet. If the packet is still not successfully decodedthen at step 15-11, a NAK is sent on the secondary acknowledgementchannel.

[0098] Sub-Packet Symbol Selection

[0099] Encoder packets are transmitted as one or more sub-packets. Thesymbols in a sub-packet may be formed by scrambling and interleaving theturbo encoder output sequence and selecting specific sequences ofsymbols from the interleaved sequence. The resulting sub-packet sequenceis a binary sequence of symbols for the modulator.

[0100] Symbol selection for the sub-packets shall be equivalent to anapproach where they are selected from a sequence of concatenatedinterleaver output sequences as described below. Let:

[0101] k be the sub-packet index;

[0102] N_(EP) be the number of bits in the encoder packet (N_(EP)=384,768, 1536, 2304, 3072, or 3840);

[0103] N_(Walsh,k) be the number of 32-chip Walsh channels for the k-thsub-packet;

[0104] N_(slots,k) be the number of 1.25-ms slots for the k-thsub-packet;

[0105] m_(k) be the modulation index for the k-th sub-packet (m_(k)=2for QPSK, 3 for 8-PSK, and 4 for 16-QAM); and

[0106] SPID_(k) be the sub-packet ID for the Y-th sub-packet(SPID_(k)=0, 1, 2, or 3).

[0107] Also, let the symbols in the concatenated sequence of interleavedsymbols be numbered from zero. Then, the selected symbols for the k-thsub-packet shall be a sequence of

L _(k)=48N _(Walsh,k) N _(dote.k) m _(k)

[0108] consecutive symbols starting at symbol F_(k), where

F _(k)=(SPID _(k) L _(k))mod(5N _(EP)).

[0109] The N_(EP), N_(Walsh,k), N_(slots,k), and m_(k) parameters arespecified in above.

[0110] A sub-packet ID of 0 shall be used to identify the firstsub-packet. The other sub-packets may be sent with sub-packet IDs of 1,2, or 3. The sub-packet IDs do not have to be sent sequentially and avalue can be used more than once. Typically, the sub-packet ID for thek-th non-initial sub-packet should be selected to minimize

min{x, 5N_(EP)−x}

[0111] where

x=|F _(k)−(F _(k−1) +L _(k−1))mod(5N _(EP))|.

[0112] When ARQ_Mode_ID=1, the first re-transmit sub-packet with sizeL_(k) is further split into 8 smaller split-sub-packets for punctureonto the (k+j)-th sub-packet with size (L_(k+j)−N_(EP(k+j)))8, thestarting symbol for j-th split-sub-packet is at location(L_(k)j)mod(5N_(Ej′k)), j=1,2, . . . , 8. The split-sub-packet puncturelocation is defined as (N_(EP(k+j))+8i)-th bit of (k+j)-th sub-packet,where i=0, 1, . . . , (L_(k+J)−N_(EP(k+J)))/8. Modulation Numerousmodifications and variations of the present invention are possible inlight of the above teachings. It is therefore to be understood thatwithin the scope of the appended claims, the invention may be practicedotherwise than as specifically described herein.

We claim:
 1. A method of performing packet re-transmission comprising:providing a first re-transmission mode and a second re-transmissionmode; and switching between executing the first re-transmission mode andexecuting the second re-transmission mode.
 2. A method according toclaim 1 wherein the first re-transmission mode is a parallelre-transmission mode and the second re-transmission mode is a stop andwait (SAW) mode.
 3. A method according to claim 2 wherein a switch fromthe first mode to the second mode occurs after transmission of apredetermined number of first mode transmissions in respect of a givenpacket.
 4. A method according to claim 2 wherein a switch from the firstmode to the second mode occurs as a function of one or more systemparameters.
 5. A method according to claim 4 wherein the one or moresystem parameters comprise a receiver buffer occupancy by first modecontent.
 6. A method according to claim 5 wherein the switch from thefirst mode to the second mode occurs when the receiver buffer occupancyexceeds a threshold.
 7. A method according to claim 2 wherein the SAWmode comprises: defining a plurality of re-transmit packets for a packetto be re-transmitted, each having different redundancies; and insertingthe re-transmit packets one at a time into a normal packet flow in placeof normal packets.
 8. A method according to claim 2 wherein the parallelre-transmission mode comprises: defining at least one re-transmit packetfor a packet to be re-transmitted; dividing each re-transmit packet intoa respective plurality sub-packets; transmitting a subset of thesub-packets of one of the re-transmit packets using a transmissionchannel parallel to a normal packet flow.
 9. A method according to claim8 wherein the parallel re-transmission mode is a non-complete puncture(NCP) mode in which transmitting a subset of the sub-packets of one ofthe re-transmit packets using a transmission channel parallel to anormal packet flow comprises inserting the subset of the sub-packets ofone of the re-transmit packets into one or more normal packets of anormal packet flow by puncturing the one or more normal packets withbits from the subset of sub-packets.
 10. A method according to claim 9wherein each re-transmit packet contains systematic content from anoriginal packet with different redundancies.
 11. A method according toclaim 1 further comprising: transmitting control information indicatingwhich of the first re-transmission mode and second re-transmission modeis a current mode of operation of re-transmission.
 12. A methodaccording to claim 2 further comprising: transmitting controlinformation indicating for SAW mode which re-transmit packet is beingtransmitted.
 13. A method according to claim 9 further comprising:wherein for a given NCP transmission, the subset of sub-packets can havea variable size, the method further comprising transmitting controlinformation indicating for NCP mode how many NCP sub-packets are in thesubset.
 14. A method according to claim 9 wherein the entire subset ispunctured into a single normal packet.
 15. A method according to claim 1further comprising: providing a first acknowledgement channel in respectof the first mode and a second acknowledgement channel in respect of thesecond mode.
 16. A method according to claim 15 further comprising:performing a switch between modes as a function of the firstacknowledgement channel.
 17. A method according to claim 15 wherein aswitch between modes as a function of the first acknowledgement channelis performed after a predetermined number of negative acknowledgementsare received in respect of first mode operation.
 18. A method accordingto claim 15 further comprising: performing a switch between modes as afunction of the second acknowledgement channel.
 19. A method accordingto claim 18 wherein a switch between modes as a function of the secondacknowledgement channel is performed after a predetermined number ofnegative acknowledgements are received in respect of second modeoperation.
 20. A transmitter adapted to performing packetre-transmission by: providing a first re-transmission mode and a secondre-transmission mode; and switching between executing the firstre-transmission mode and executing the second re-transmission mode. 21.A transmitter according to claim 20 wherein the first re-transmissionmode is a parallel retransmission mode and the second re-transmissionmode is a stop and wait (SAW) mode.
 22. A transmitter according to claim21 wherein a switch from the first mode to the second mode occurs aftertransmission of a predetermined number of first mode transmissions inrespect of a given packet.
 23. A transmitter according to claim 21wherein a switch from the first mode to the second mode occurs as afunction of one or more system parameters.
 24. A transmitter accordingto claim 23 wherein the one or more system parameters comprise areceiver buffer occupancy by first mode content.
 25. A transmitteraccording to claim 20 wherein the SAW mode comprises; defining aplurality of re-transmit packets for a packet to be re-transmitted, eachhaving different redundancies; and inserting the re-transmit packets oneat a time into a normal packet flow in place of normal packets.
 26. Atransmitter according to claim 21 wherein the parallel re-transmissionmode comprises: defining at least one re-transmit packet for a packet tobe re-transmitted; dividing each re-transmit packet into a respectiveplurality sub-packets; transmitting a subset of the sub-packets of oneof the re-transmit packets using a transmission channel parallel to anormal packet flow.
 27. A transmitter according to claim 8 wherein theparallel re-transmission mode is an NCP mode in which transmitting asubset of the sub-packets of one of the re-transmit packets using atransmission channel parallel to a normal packet flow comprisesinserting the subset of the sub-packets of one of the re-transmitpackets into one or more normal packets of a normal packet flow bypuncturing the one or more normal packets with bits from the subset ofsub-packets.
 28. A transmitter according to claim 27 adapted to transmitcontrol information indicating which of the first and second mode is acurrent mode of operation of re-transmission, and to transmit controlinformation indicating for SAW mode which re-transmit packet is beingtransmitted.
 29. A transmitter according to claim 20 further adapted toreceive a first acknowledgement channel in respect of the first mode anda second acknowledgement channel in respect of the second mode.
 30. Atransmitter according to claim 29 further adapted to perform a switchbetween modes as a function of the first acknowledgement channel, thesecond acknowledgement channel, or a combination of the firstacknowledgement channel and the second acknowledgement channel.
 31. Apacket re-transmission system comprising: first re-transmission modemeans providing a first parallel re-transmission mode; secondre-transmission mode means providing a second stop and waitre-transmission mode; and mode switching means for switching betweenexecuting the first parallel re-transmission mode and executing thesecond stop and wait re-transmission mode.